Background People who attempt suicide often display cognitive impairments, particularly poor cognitive control. Could poor cognitive control contribute to high suicide rates in old age? A component of cognitive control, cognitive inhibition—active suppression of task‐irrelevant processing—is very sensitive to aging and has been linked to attempted suicide. We investigated cognitive inhibition in older high‐lethality suicide attempters, closely resembling suicide victims, as well as low‐lethality attempters, and control groups with and without depression and suicidal ideation. Methods A total of 102 participants aged 60 years and older (17 psychiatrically healthy control subjects, 38 depressed control subjects, 16 suicide ideators, 14 low‐lethality suicide attempters, and 17 high‐lethality suicide attempters) underwent comprehensive clinical and cognitive assessments. They completed the Delis–Kaplan Executive Function System Color‐Word Interference Test, a validated modification of the Stroop test. Results High‐lethality suicide attempters demonstrated a distinct pattern of cognitive inhibition deficits. Compared with psychiatrically healthy control subjects and suicide ideators, high‐lethality attempters took longer to complete inhibition trials, even after accounting for potential confounding factors (age, education, Mini mental state examination score, information processing speed, and accuracy). Compared with non‐suicidal depressed and healthy control subjects, low‐lethality suicide attempters committed more uncorrected errors; however, this difference was not specific to the inhibition condition. Conclusions Older suicide attempters are a cognitively heterogeneous group. Poor cognitive control in high‐lethality attempters may undermine their ability to solve real‐life problems, precipitating a catastrophic accumulation of stressors. Meanwhile, low‐lethality attempters' poor performance may reflect a careless approach to the task or faulty monitoring. Copyright © 2014 John Wiley & Sons, Ltd.